Motor control device and motor drive device

ABSTRACT

A sampling period of information according to a load state of an alternating-current motor is controlled so as to be variable with respect to a carrier period of a PWM circuit, and a predetermined arithmetic operation for aggregating information sampled in one period of the carrier period is performed in a separate arithmetic circuit from a CPU. Thereby, in a situation where the rotation of the alternating-current motor becomes too fast with respect to the carrier period, motor rotation control for suppressing a sudden fluctuation of a motor load can be performed by faster reaction while suppressing an increase in an arithmetic control load of a CPU.

TECHNICAL FIELD

The invention relates to a motor control that performs PWM (Pulse-widthmodulation) control on the supply of a motor current to analternating-current motor in accordance with a drive command andfeedback information, particularly, a sampling technique of feedbackinformation for a carrier period of PWM, and relates to a techniqueeffective in a case of application to PWM motor control of, for example,an electric vehicle (EV) or a hybrid vehicle (HV).

BACKGROUND ART

In PWM control for an alternating-current motor of an EV or an HV, acurrent command value generated on the basis of a motor control logicsuch as vector control which is mounted in a control circuit is given toa PWM circuit, to thereby generate a PWM pulse for applying an outputvoltage having any amplitude and phase from an inverter to analternating-current motor. Control of a torque which is generated by theinteraction of a motor current with a magnetic flux which is interlinkedwith a winding of the alternating-current motor is required forcontrolling the rotational speed of an alternating-current motor and theposition of a rotor at high speed. For this reason, the control circuitgenerates a current command value to a drive command for each phasewhile referring to current information which is fed back from a feedbackloop of the motor current or position information of the rotor, andgives the generated value to the PWM circuit. Such general PWM controlfor the alternating-current motor is disclosed in, for example, PTL 1.

In the PWM control for the alternating-current motor, the rotation speedof the alternating-current motor is sufficiently slow in a carrierperiod of the PWM circuit. Thus, in case that a motor currentacquisition period corresponding to the carrier period is generated inthe acquisition of the motor current from the feedback loop, it ispossible to acquire a sinusoidal motor current, and to reflectarithmetic results based on the fed-back motor current or the like inthe PWM pulse. For example, in case that a sinusoidal wave isrepresented by more than twelve divisions with respect to a carrierperiod having a frequency of 10 kHz, the rotation speed of thealternating-current motor can attain up to 833 Hz.

CITATION LIST Patent Literature

PTL 1: Domestic Re-publication of PCT Patent Application No. 2010/109964

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

The inventor has examined a case where the rotation speed of analternating-current motor becomes too fast with respect to a carrierperiod of a PWM circuit. In case that the rotation of thealternating-current motor becomes too fast with respect to the carrierperiod, a motor current is not able to be acquired in a sinusoidalshape. In this case, the shortening of a current acquisition periodmakes it possible to acquire a current, but a PWM pulse to be reflectedis dependent on the carrier period, and thus feedback current valuesacquired during the carrier period have to be arithmetically calculatedcollectively by filtering or averaging, to thereby reflect the resultantin a duty of the PWM pulse. In this case, arithmetic responsiveness offiltering or averaging is dependent on a current acquisition period or afilter gain, and thus controllability deteriorates as compared to normalcontrol. In addition, in a high-rotation region of thealternating-current motor, since a load of arithmetic control of a CPUhas a tendency to become larger to make matters worse, the shortening ofa sampling interval of a feedback current causes a further increase inthe load of the CPU. Thus, it was made clear that there might be aconcern of the sampling interval of the feedback current not being ableto be sufficiently shortened. Particularly, a situation where therotation speed of the alternating-current motor which is a travelingdrive source of an EV or an HV becomes too fast with respect to thecarrier period is assumed to be generated by the skidding of a wheel dueto a slip. This may be an induction factor for an accident caused bysudden acceleration, abrupt steering, road surface freezing, and thelike. Thus, a sudden fluctuation of the load has to be suppressed by atleast faster reaction to the skidding of a wheel. Therefore, it isnecessary to control the rotational speed of a motor in a direction inwhich a sudden fluctuation of a load is suppressed by faster reaction toa situation where the rotation of the alternating-current motor becomestoo fast with respect to the carrier period.

The foregoing and other problems and novel features for solving theproblems will be made clearer from the description of the presentspecification and the accompanying drawings.

Means for Solving the Problems

The following is a brief description of the representative embodimentsdisclosed in the present application.

That is, a sampling period of information according to a load state ofan alternating-current motor is controlled so as to be variable withrespect to a carrier period of a PWM circuit, and a predeterminedarithmetic operation for aggregating information sampled in one periodof the carrier period is performed in a separate arithmetic circuit froma CPU.

Effects of the Invention

The following is a brief description of an effect obtained by therepresentative embodiments of the invention disclosed in the presentapplication.

That is, in a situation where the rotation of the alternating-currentmotor becomes too fast with respect to the carrier period, motorrotation control for suppressing a sudden fluctuation of a motor loadcan be performed by faster reaction while suppressing an increase in anarithmetic control load of a CPU.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a motor drivedevice.

FIG. 2 is a block diagram illustrating, in principle, a PWM controlfunction for vector control of an alternating-current motor in a CPU andan arithmetic function of an accelerator.

FIG. 3 is a diagram conceptually illustrating a case where a samplingperiod in which motor current values iv and iw and an electrical angle θare acquired and a carrier period are coincident with each other.

FIG. 4 is a diagram illustrating a case where a motor drive current isnot easily represented by a sinusoidal wave through a PWM pulse in amotor current having a high frequency due to a fast motor rotation.

FIG. 5 is a diagram conceptually illustrating a process in case that thesampling period in which the motor current values iv and iw and theelectrical angle θ are acquired is made shorter than the carrier period.

FIG. 6 is a block diagram illustrating a configuration of an acceleratorfor performing synchronous control of the sampling period.

FIG. 7 is a flow diagram illustrating a processing procedure ofautonomous synchronous control of the sampling period together with asynchronous control procedure of the sampling period in a CPU.

FIG. 8 is a diagram illustrating a processing mode for shortening thesampling period halfway in case that a great load fluctuation isdetected in the middle of the carrier period in the autonomoussynchronous control of the sampling period.

FIG. 9 is a diagram illustrating a control mode in the skidding of awheel and the return thereof to a normal rotation.

FIG. 10 is a diagram illustrating an operation mode in case that thecarrier period is changed together with the sampling period with respectto the sudden fluctuation of a load.

FIG. 11 is a diagram illustrating a processing mode in which the numberof times of sampling with the carrier period is made variable inaccordance with a motor load (motor rotation speed) in the synchronouscontrol of the sampling period in a CPU.

FIG. 12 is a block diagram illustrating a configuration of theaccelerator in which a CPU is burdened with a control function of acontrol circuit in the accelerator of FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION 1. Summary of the Embodiments

First, summary of representative embodiments of the invention disclosedin the application will be described. Reference numerals in drawings inparentheses referred to in description of the summary of therepresentative embodiments just denote components included in theconcept of the components to which the reference numerals aredesignated.

[1] <Making Sampling Period of Load Fluctuation Variable with Respect toPWM Carrier Period>

A motor control device (13) according to a representative embodimentincludes a PWM circuit (23) for performing switch control on an inverter(10) that outputs a drive current to an alternating-current motor (2)through a PWM pulse signal (Pu, Pv, Pw), a CPU (20) that performsfeedback control on a duty of the PWM pulse signal, and an arithmeticunit (26, 26A), in which a sampling period of feedback information (iv,iw, θ) is made variable, and which performs predetermined arithmeticprocessing for aggregating the feedback information acquired in thesampling period shorter than a carrier period of the PWM circuit in acomparison target for one period of the carrier period in case that apredetermined load fluctuation is generated in the alternating-currentmotor. The CPU controls the duty of the PWM pulse signal after thepredetermined load fluctuation is generated, on the basis of anarithmetic result in the arithmetic unit and the drive command value.

According to this, it is possible to acquire the feedback information ina period shorter than the carrier period in accordance with apredetermined fluctuation of a motor load, and to burden the arithmeticunit with an arithmetic operation for aggregating a plurality of piecesof feedback information, acquired in the carrier period alone, in thecomparison target for one period of the carrier period. Therefore, in asituation where the rotation of the alternating-current motor becomestoo fast with respect to the carrier period, motor rotation control forsuppressing a sudden fluctuation of a motor load can be performed byfaster reaction while suppressing an increase in an arithmetic controlload of a CPU.

[2] <Information of Motor Current and Rotor Angle of Motor>

In item 1, the feedback information is a motor current value (iv, iw)which is obtained by performing AD conversion on a current which is fedback from an alternating-current motor and a rotor rotation angle value(θ) which is obtained from a rotor position of the alternating-currentmotor.

According to this, the motor control device is suitable for vectorcontrol of the alternating-current motor.

[3] <Control Circuit Detects Load Fluctuation to Change Sampling Period>

In item 2, in case that a predetermined load fluctuation is generated inthe alternating-current motor, the control unit (26) includes a controlcircuit (46) that controls a sampling period of feedback information soas to be variable, and an arithmetic circuit (47) that performs thepredetermined arithmetic processing. The control circuit determineswhether a predetermined load fluctuation is generated in thealternating-current motor, shortens a period in which the feedbackinformation is acquired until control of the alternating-current motorfollows the load fluctuation in case that the load fluctuation isdetermined to be generated, and performs control for sequentiallyreturning the period in which the feedback information is acquired to areference value in case that the control of the alternating-currentmotor follows the load fluctuation.

According to this, it is possible to burden the control circuit withcontrol of the acquisition period of the feedback information until thealternating-current motor skids due to a slip or the like and thenrecovers. It is possible to reduce a burden of the CPU in this point.

[4] <CPU Initializes Acquisition Period of Feedback Information>

In item 3, the CPU initializes the period in which the feedbackinformation is acquired, and the control circuit sets the initializedperiod to a control target.

According to this, separately from the control of the acquisition periodof the feedback information in the control circuit, the CPU requiressetting control of the carrier period of the PWM circuit in accordancewith a relationship with a rotation torque required for the feedbackcontrol, and thus it is economical, in view of a system, for the CPU toinitialize a period in which the feedback information is acquired in therelationship with the rotation torque.

[5] <Load Fluctuation Sensing in Control Circuit (Rotor Angle, MotorCurrent)>

In item 3, the control circuit senses the predetermined load fluctuationfrom the rotor rotation angle value or the motor current value.

According to this, it is possible to easily acquire the fluctuation ofthe motor load without imposing a burden on the CPU.

[6] <Load Fluctuation Sensing in Control Circuit (State DetectionInformation of Traveling Surface)>

In item 5, the control circuit further predicts the predetermined loadfluctuation from state detection information (RDST) of a travelingsurface that receives a rotational force of the alternating-currentmotor.

According to this, the fluctuation of the motor load is predicted, andthus motor rotation control for suppressing a sudden fluctuation of themotor load can be performed by faster reaction.

[7] <Filter Arithmetic Operation, Averaging Arithmetic Operation>

In item 3, the predetermined arithmetic processing in the arithmeticcircuit includes coordinate conversion processing (coordinate conversionportion 40) for converting the motor current value and the rotorrotation angle value into a two-phase current value, and filterarithmetic processing or average arithmetic processing (aggregatearithmetic portions 41 d and 41 q) for the two-phase current value onwhich coordinate conversion is performed.

According to this, the motor control device is suitable for a case wherethe alternating-current motor is driven using coordinate conversion by adirect-current power supply, and it is possible to easily aggregate aplurality of pieces of information by using the filter arithmeticprocessing or the average arithmetic processing.

[8] <Arithmetic Gain Control in Control Circuit>

In item 7, the control circuit further changes a gain of the filterarithmetic processing or the average arithmetic processing in thearithmetic circuit, as necessary, in case that the period in which thefeedback information is acquired is set to be short, and performscontrol for returning the gain of the filter arithmetic processing orthe average arithmetic processing to the initial value in case that theperiod in which the feedback information is acquired is returned to thereference value.

According to this, it is possible to decrease the gains in accordancewith an increase in the number of acquisitions of the feedbackinformation so that a response does not become sensitive withoutimposing a burden on the CPU, or to keep the gains unchanged due to afast response in case that the number of acquisitions of the feedbackinformation increases.

[9] <Initialization of Gain in CPU>

In item 8, the CPU initializes the gain of the filter arithmeticprocessing or the average arithmetic processing, and the control circuitsets the initialized gain to a control target.

According to this, separately from the control of the acquisition periodof the feedback information in the control circuit, the CPU alsorequires gain setting depending on the setting of the carrier period ofthe PWM circuit in accordance with a relationship with a rotation torquerequired for the feedback control, and thus it is economical, in view ofa system for the CPU to initialize a gain of the filter arithmeticprocessing or the average arithmetic processing in the relationship withthe rotation torque.

[10] <Sampling Period Control in Control Circuit; Startup TriggerInterval of AD Conversion>

In item 7, the control circuit controls an AD conversion startup triggerinterval of AD conversion processing of the fed-back current and afetching interval of the rotor rotation angle value to the arithmeticcircuit, to thereby determine the period in which the feedbackinformation is acquired.

According to this, in follow-up control, it is possible to easilycontrol the sampling period of the feedback information for obtainingthe feedback information without imposing a burden on the CPU.

[11] <CPU Detects Load Fluctuation to Change Sampling Period>

In items 11 to 16, a function of the follow-up control portion in items3 to 10 is replaced by a CPU. In item 2, the control unit (26A) includesan arithmetic circuit (47) that performs the predetermined arithmeticprocessing, and the CPU controls a sampling period of feedbackinformation so as to be variable, determines whether a predeterminedload fluctuation is generated in the alternating-current motor, shortensa period in which the feedback information is acquired until control ofthe alternating-current motor follows the load fluctuation in case thatthe load fluctuation is determined to be generated, and returns theacquisition period of the feedback information to a reference value incase that the control of the alternating-current motor follows the loadfluctuation.

According to this, a burden of the CPU increases in the control of theacquisition period of the feedback information as compared to item 3,but it is possible to cope with the burden flexibly through software ofthe CPU.

[12] <Load Fluctuation Sensing in CPU (Rotor Angle, Motor Current)>

In item 11, the CPU senses the predetermined load fluctuation from rotorlocation information of a motor or a motor current.

According to this, a burden of the CPU increases as compared to item 5,but it is possible to easily acquire the fluctuation of the motor load.

[13] <Load Fluctuation Sensing in CPU (State Detection Information ofTraveling Surface)>

In item 12, the CPU further predicts the predetermined load fluctuationfrom state detection information of a traveling surface that receives arotational force of the alternating-current motor.

According to this, a burden of the CPU increases as compared to item 6,but the fluctuation of the motor load is predicted, and thus motorrotation control for suppressing a sudden fluctuation of the motor loadcan be performed by faster reaction.

[14] <Filter Arithmetic Operation, Averaging Arithmetic Operation>

In item 11, the predetermined arithmetic processing in the arithmeticcircuit includes coordinate conversion processing for converting themotor current value and the rotor rotation angle value into a two-phasecurrent value, and filter arithmetic processing or average arithmeticprocessing for the two-phase current value on which coordinateconversion is performed.

According to this, the motor control device is suitable for a case wherethe alternating-current motor is driven using coordinate conversion by adirect-current power supply, and it is possible to easily aggregate aplurality of pieces of information by using the filter arithmeticprocessing or the average arithmetic processing.

[15] <Arithmetic Gain Control in CPU>

In item 14, the CPU changes a gain of the filter arithmetic processingor the average arithmetic processing in the arithmetic circuit, asnecessary, in case that the period in which the feedback information isacquired is set to be short, and performs control for returning the gainof the filter arithmetic processing or the average arithmetic processingto the initial value in case that the period in which the feedbackinformation is acquired is returned to the reference value.

According to this, a burden of the CPU increases as compared to item 8,but, it is possible to decrease the gains in accordance with an increasein the number of acquisitions of the feedback information so that aresponse does not become sensitive without imposing a burden on the CPU,or to keep the gains unchanged due to a fast response in case that thenumber of acquisitions of the feedback information increases.

[16] <Sampling Period in CPU; Startup Trigger Interval of AD Conversion>

In item 14, the CPU controls an AD conversion startup trigger intervalof AD conversion processing of the fed-back current and a fetchinginterval of the rotor rotation angle value to the arithmetic circuit, tothereby determine the acquisition period of the feedback information.

According to this, in the follow-up control, a burden of the CPUincreases as compared to item. 10, but it is possible to easily controlthe sampling period of the feedback information for obtaining thefeedback information.

[17] <Microcomputer>

In any one of items 1 to 16, the motor control device is constituted bya microcomputer which is formed as a semiconductor integrated circuit ina silicon substrate.

According to this, it is possible to contribute to a reduction in thesize of the motor control device.

[18] <Making Sampling Period of Load Fluctuation Variable with respectto PWM Carrier Period>

A motor drive device (1) according to another embodiment different fromthat in items 1 to 18, the device driving an alternating-current motor(2) for vehicle traveling, includes an inverter (10) that supplies amotor current to the alternating-current motor, a motor control device(13) that performs feedback control on a motor current which is outputby the inverter on the basis of a drive command. The motor controldevice includes a PWM circuit (23) that performs switch control on theinverter through a PWM pulse signal (Pu, Pv, Pw), a CPU (20) thatperforms feedback control on a duty of the PWM pulse signal, and anarithmetic unit (26, 26A), in which a sampling period of feedbackinformation (id, iq, θ) is made variable, and which performspredetermined arithmetic processing for aggregating a plurality ofpieces of the feedback information acquired in the sampling periodshorter than a carrier period of the PWM circuit in a comparison targetfor one period of the carrier period in case that a predetermined loadfluctuation is generated in the alternating-current motor. The CPUcontrols the duty of the PWM pulse signal after the predetermined loadfluctuation is generated, on the basis of an arithmetic result in thearithmetic unit and the drive command value.

According to this, it is possible to acquire the feedback information ina period shorter than the carrier period in accordance with apredetermined fluctuation of a motor load, and to burden the arithmeticunit with an arithmetic operation for aggregating a plurality of piecesof feedback information, acquired in the carrier period alone, in thecomparison target for one period of the carrier period. Therefore, in asituation where the rotation of the alternating-current motor becomestoo fast with respect to the carrier period, motor rotation control forsuppressing a sudden fluctuation of a motor load can be performed byfaster reaction while suppressing an increase in an arithmetic controlload of a CPU. Thus, it is possible to suppress a sudden fluctuation ofthe load by at least faster reaction to the skidding of a wheel, and tocontribute to prevent an accident which is generated by the skid of awheel due to a slip caused by sudden acceleration, abrupt steering,freezing road surface, and the like in an EV, an HV or the like.

[19] <Information of Motor Current and Rotor Angle of Motor>

In item 18, the feedback information is a motor current value which isobtained by performing AD conversion on a current which is fed back fromthe alternating-current motor and a rotor rotation angle value which isobtained from a rotor position of the alternating-current motor.

According to this, the same operational effect as that of item 2 isexhibited.

[20] <Control Circuit Detects Load Fluctuation to Change SamplingPeriod>

In item 19, the control unit (26) includes a control circuit (46) thatcontrols a sampling period of feedback information so as to be variablein case that a predetermined load fluctuation is generated in thealternating-current motor, and an arithmetic circuit (47) that performsthe predetermined arithmetic processing. The control circuit determineswhether a predetermined load fluctuation is generated in thealternating-current motor, shortens a period in which the feedbackinformation is acquired until control of the alternating-current motorfollows the load fluctuation in case that the load fluctuation isdetermined to be generated, and performs control for sequentiallyreturning the period in which the feedback information is acquired to areference value in case that the control of the alternating-currentmotor follows the load fluctuation.

According to this, the same operational effect as that of item 2 isexhibited.

[21] <CPU Initializes Acquisition Period of Feedback Information>

In item 20, the CPU initializes the period in which the feedbackinformation is acquired, and the follow-up control portion sets theinitialized period to a control target.

According to this, the same operational effect as that of item 4 isexhibited.

[22] <Load Fluctuation Sensing in Control Circuit (Rotor Angle, MotorCurrent)>

In item 20, the control circuit senses the predetermined loadfluctuation from the rotor rotation angle value or the motor currentvalue.

According to this, the same operational effect as that of item 5 isexhibited.

[23] <Load Fluctuation Sensing in Control Circuit (State DetectionInformation of Traveling Surface)>

In item 22, the control circuit further predicts the predetermined loadfluctuation from state detection information of a traveling road surfaceof a vehicle.

According to this, the same operational effect as that of item 6 isexhibited.

[24] <Filter Arithmetic Operation, Averaging Arithmetic Operation>

In item 20, the predetermined arithmetic processing in the arithmeticcircuit includes coordinate conversion processing for converting themotor current value and the rotor rotation angle value into a two-phasecurrent value, and filter arithmetic processing or average arithmeticprocessing for the two-phase current value on which coordinateconversion is performed.

According to this, the same operational effect as that of item 7 isexhibited.

[25] <Arithmetic Gain Control in Control Circuit>

In item 24, the control circuit further changes a gain of the filterarithmetic processing or the average arithmetic processing in thearithmetic circuit, as necessary, in case that the period in which thefeedback information is acquired is set to be short, and performscontrol for returning the gain of the filter arithmetic processing orthe average arithmetic processing to the initial value in case that theperiod in which the feedback information is acquired is returned to thereference value.

According to this, the same operational effect as that of item 8 isexhibited.

[26] <Initialization of Gain in CPU>

In item 25, the CPU initializes the gain of the filter arithmeticprocessing or the average arithmetic processing, and the control circuitsets the initialized gain to a control target.

According to this, the same operational effect as that of item 9 isexhibited.

[27] <Sampling Period Control in Control Circuit; Startup TriggerInterval of AD Conversion>

In item 24, the control circuit controls an AD conversion startuptrigger interval of AD conversion processing of the fed-back current anda fetching interval of the rotor rotation angle value to the arithmeticcircuit, to thereby determine the period in which the feedbackinformation is acquired.

According to this, the same operational effect as that of item 10 isexhibited.

[28] <CPU Detects Load Fluctuation to Change Sampling Period>

In items 28 to 33, a function of the follow-up control portion in items20 to 27 is replaced by a CPU. In item 19, the control unit (26A)includes an arithmetic circuit (47) that performs the predeterminedarithmetic processing. The CPU (20) controls a sampling period offeedback information so as to be variable, determines whether apredetermined load fluctuation is generated in the alternating-currentmotor, shortens a period in which the feedback information is acquireduntil control of the alternating-current motor follows the loadfluctuation in case that the load fluctuation is determined to begenerated, and returns the period in which the feedback information isacquired to a reference value in case that the control of thealternating-current motor follows the load fluctuation.

According to this, the same operational effect as that of item 11 isexhibited.

[29] <Load Fluctuation Sensing in CPU (Rotor Angle, Motor Current)>

In item 29, the CPU senses the predetermined load fluctuation from therotor rotation angle value or the motor current value.

According to this, the same operational effect as that of item 12 isexhibited.

[30] <Load Fluctuation Sensing in CPU (Road Surface Reflectance)>

In item 29, the CPU further predicts the predetermined load fluctuationfrom state detection information of a traveling road surface of avehicle.

According to this, the same operational effect as that of item 13 isexhibited.

[31] <Filter Arithmetic Operation, Averaging Arithmetic Operation>

In item 28, the predetermined arithmetic processing in the arithmeticcircuit includes coordinate conversion processing for converting themotor current value and the rotor rotation angle value into a two-phasecurrent value, and filter arithmetic processing or average arithmeticprocessing for the two-phase current value on which coordinateconversion is performed.

According to this, the same operational effect as that of item 14 isexhibited.

[32] <Arithmetic Gain Control in CPU>

In item 31, the CPU changes a gain of the filter arithmetic processingor the average arithmetic processing in the arithmetic circuit, asnecessary, in case that the period in which the feedback information isacquired is set to be short, and performs control for returning the gainof the filter arithmetic processing or the average arithmetic processingto the initial value incase that the period in which the feedbackinformation is acquired is returned to the reference value.

According to this, the same operational effect as that of item 15 isexhibited.

[33] <Sampling Period Control in CPU; Startup Trigger Interval of ADConversion>

In item 31, the CPU controls an AD conversion startup trigger intervalof AD conversion processing of the fed-back current and a fetchinginterval of the rotor rotation angle value to the arithmetic circuit, tothereby determine the acquisition period of the feedback information.

According to this, the same operational effect as that of item 16 isexhibited.

[34] <ECU>

In any of items 10 to 17, the motor control device constitutes an ECUwhich is connected to an in-vehicle network.

According to this, the motor drive device is suitable for an EV or anHV.

2. Further Detailed Description of the Embodiments

A further detailed description of the embodiments will be given.Meanwhile, in all the drawings for the purpose of describing a mode forcarrying out the invention, components having the same functions aredenoted by the same reference numerals and signs, and thus thedescription thereof will not be repeated.

<<Motor Drive Device>>

FIG. 1 illustrates an example of a motor drive device. A motor drivedevice 1 shown in the drawing is a device that drives analternating-current motor (MT) 2 which is a motive power source for EVor HV traveling. Although not particularly limited, a motor shaft of thealternating-current motor 2 is connected to a wheel 4 through atransmission 3. Further, the motor shaft of the alternating-currentmotor 2 has a resolver for detecting its rotation angle connectedthereto. Although particularly not shown in the drawing, in a case ofin-wheel motor drive, an alternating-current motor and a resolver areprovided independently for each wheel.

The motor drive device 1 includes a 3-phase voltage-type inverter 10using six insulated gate bipolar transistors (IGBT), a pre-driver 11, aresolver digital converter (RD converter) 12, a microcomputer (MCU) 13which is an example of the motor control device, and a networktransceiver (TRC) 14 which is connected to an in-vehicle network 6 suchas CAN, and constitutes one ECU (Electronic Control Unit).

A drive current of the inverter 10 is detected as motor currents Iv andIw, for example, by a current sensor 14, and is fed back to themicrocomputer 13.

The resolver 5 inputs an excitation signal Smg from the RD converter 12,to output sine and cosine resolver signals Srs from a detection coil inaccordance with the angle of a rotor. The RD converter 12 generates amotor rotation phase signal Rp such as an encoder-equivalent pulsesignal from the resolver signal Srs and feeds back the generated signalto the microcomputer 13.

Although not particularly limited, the microcomputer 13 is formed in onesemiconductor substrate such as single crystal silicon by a CMOS circuitmanufacturing technique or the like.

The microcomputer 13 is an example of the motor control device thatperforms feedback control on the motor current which is output by theinverter on the basis of a drive command. Here, the pre-driver 11 andthe RD converter 12 serve as external components of the microcomputer13, but can also be built into the microcomputer 13.

The microcomputer 13 is connected to the network transceiver 14 througha network controller (COM) 22, and receives a detection signal from asensor (SNSR) 7, or communicates with other ECUs (not shown).

The microcomputer 13 includes a CPU (Central Processing Unit) 20 as acentral processing unit that executes a program, and an internal memory(MRY) 21 which is constituted by a non-volatile memory that stores aprogram executed by the CPU 20 or control data and a RAM which is usedin a work area of the CPU 20. The microcomputer 13 includes a PWMcircuit (PWM) 23 that outputs 3-phase PWM pulse signals Pu, Pv, and Pwfor driving the inverter 10 to the pre-driver 11. Further, themicrocomputer 13 includes an AD converter (ADC) 24 that converts ananalog signal to a digital signal, a counter (COUNT) 25 that inputs andcounts a phase signal, and an accelerator (ACCL) 26 as an arithmeticcircuit that performs a required arithmetic operation and arithmeticcontrol. Meanwhile, a circuit block inside the microcomputer 13 iscapable of a signal interface through an internal bus 27 which isrepresentatively shown.

The AD converter 24 performs AD conversion on the motor currents Iv andIw of the motor in accordance with a sampling period indicated from theCPU 20 or the accelerator 26 to obtain motor current values iv and iw,and outputs the resultant to the accelerator 26 or the like. The counter25 counts the motor rotation phase signal Rp which is input through theRD converter 12 to acquire an electrical angle (rotor rotation anglevalue indicating a rotor position of the motor) θ, and the acquiredelectrical angle θ is used for each required sampling period by the CPU20 or the accelerator 26. The motor current values iv and iw and theelectrical angle θ are an example serving as feedback information whichis fed back to the accelerator 26 by the driving of thealternating-current motor.

FIG. 2 illustrates, in principle, a PWM control function for vectorcontrol of the alternating-current motor in a CPU and an arithmeticfunction of the accelerator.

In a case of a vehicle, an output torque command of the motor is firstdetermined from an accelerator opening degree, a vehicle speed or thelike. In order to perform the vector control on the basis of this outputtorque command, d-axis and q-axis current command values id and iq arethen calculated as drive command values. The output torque command isgiven to the CPU 20 through, for example, the network 6, and thus theCPU 20 calculates the d-axis current command value id and the q-axiscurrent command value iq.

The d-axis current command value id and the q-axis current command valueiq which are obtained are supplied to subtracters 30 d and 30 q. Here,deviations Δid and Δiq between a present d-axis current value idc and apresent q-axis current value iqc are obtained. Regarding the obtaineddeviations Δid and Δiq, in PI arithmetic units 32 d and 32 q, a d-axisvoltage command value Vd and a q-axis voltage command value Vq arecalculated by a PI (Proportional-Integral) control arithmetic operationbased on a proportional integral algorithm. That is, the d-axis andq-axis currents idc and iqc are corrected by the sum of a P feedbackvalue obtained by multiplying the deviations Δid and Δiq by a P gain(proportional gain) and an I feedback value obtained by multiplying anintegrated value of the deviations Δid and Δiq by an I gain (integrationgain), and these values are converted into voltage command values tocalculate the d-axis and q-axis voltage commands Vd and Vq.

The calculated d-axis and q-axis voltage command values Vd and Vq aresupplied to a coordinate conversion portion 34 that performs coordinateconversion from 2-phase to 3-phase, and are subject to coordinateconversion from two axes of d and q to three axes of U, V, and W, andthus 3-phase motor drive voltage commands Vu, Vv, and Vw of which thephases are different from each other by 120 degrees are obtained. Theobtained motor drive voltage command values Vu, Vv, and Vw are convertedinto the PWM pulse signals Pu, Pv, and Pw in the PWM circuit 23. Thisconversion is performed by comparing, for example, the motor drivevoltage commands Vu, Vv, and Vw with, for example, a triangular wave ofa predetermined frequency which is a carrier signal of a predeterminedfrequency (carrier frequency), and determining the duty ratio of the PWMpulse signals Pu, Pv, and Pw. In this manner, the PWM pulse signals Pu,Pv, and Pw of each phase are formed, and these pulse signals aresupplied to the inverter 10 through the pre-driver 11.

The inverter 10 is configured to receive a direct-current voltage from abattery (not shown) between a positive-electrode line and anegative-electrode line, and to convert the received voltage into a3-phase alternating current. For example, three series circuits areconfigured to be connected to each other between the positive-electrodeline and the negative-electrode line, each of the series circuits beingcomposed of two complementary insulated gate bipolar transistors, and acoupling node between the two complementary insulated gate bipolartransistors in each series circuit serves as an output of each phase.Each of the series circuits is operated complementarily switchably inthe PWM pulse signals Pu, Pv, and Pw, and thus a 3-phase motor drivecurrent is generated. The motor drive current is supplied to the motor2, and the motor 2 is driven by an output according to the output torquecommand.

Here, the phase of the motor drive current is determined in accordancewith the electrical angle (rotor position) of the motor 2. Therefore,the resolver 5 as an angle sensor is installed in the motor 2, theresolver signal Srs is output from the resolver 5 to the RD converter12, and the RD converter 12 generates the motor rotation phase signalRp.

The motor rotation phase signal Rp is counted in the counter 25 and hasan offset error added thereto, and thus the electrical angle θ of thealternating-current motor 2 is calculated. The electrical angle θ issupplied to the coordinate conversion portion 34 and thus is used inphase control of the motor drive voltage commands Vu, Vv, and Vw. Inaddition, the electrical angle θ is supplied to the coordinateconversion portion 40 of the accelerator 26, and is used in thecoordinate conversion of the motor current values iv and iw from 3-phaseto 2-phase.

The coordinate conversion portion 40 performs coordinate conversion onthe motor current values iv and iw, which are output from the ADconverter 24, to the d and q-axes using the electrical angle θ, andcalculates a d-axis current value idm and a q-axis current value iqm.The coordinate conversion arithmetic portion 34 may acquire theelectrical angle θ required for a coordinate conversion arithmeticoperation for each carrier period of the PWM circuit 23. On the otherhand, the coordinate conversion portion 40 needs to acquire theelectrical angle θ required for a coordinate conversion arithmeticoperation for each sampling period of the motor current values iv andiw.

The d-axis current value idm and the q-axis current value iqm which arecalculated are supplied to aggregate arithmetic portions 41 d and 41 q,and are subject to a predetermined arithmetic operation. The arithmeticresults are supplied to the above-mentioned subtracters 30 d and 30 q asa present d-axis current value id and a present q-axis current value iq.

Here, a period in which the motor current values iv and iw and theelectrical angle θ are generated is not limited to a carrier period unitof the PWM circuit 23, and is set to a short period of one severalth ofthe carrier period, to take into consideration the drastic loadfluctuation of the alternating-current motor 2 so as to be capable offollowing the motor control. In case that a predetermined loadfluctuation occurs in the alternating-current motor 2, the motor currentvalues iv and iw and the electrical angle θ are acquired at an intervalshorter than the carrier period of the PWM circuit 23, and the aggregatearithmetic portions 41 d and 41 q perform predetermined arithmeticprocessing, such as filter arithmetic processing or average arithmeticprocessing, for aggregating a plurality of d-axis current values idm andq-axis current values iqm for one period of the carrier period on whichthe coordinate conversion arithmetic operation is sequentially performedin the acquisition period, in a comparison target for one period of thecarrier period. Meanwhile, in case that the sampling period of the motorcurrent values iv and iw and the electrical angle θ is set to be equalto the carrier period of the PWM circuit 23, the filter arithmeticprocessing or the average arithmetic processing for the aggregation hasno substantial meaning, and sampled information is output to thepost-stage as it is.

Here, a relationship between the sampling period in which the motorcurrent values iv and iw and the electrical angle θ are acquired and thecarrier period will be described.

FIG. 3 conceptually illustrates a case where the sampling period inwhich the motor current values iv and iw and the electrical angle θ areacquired and the carrier period are coincident with each other. Here,fcrr is a conceptual carrier period of the PWM circuit 23, Iu is a1-phase motor current waveform, Tsm is a sampling timing of the motorcurrent, and Pu and Pub are 1-phase complementary PWM pulse signals. Ina PWM operation in this example, the motor current values iv and iw andthe electrical angle θ are sampled one time for each carrier period, anda coordinate conversion arithmetic operation (vector arithmeticoperation) is performed on the resultant. The result is reflected in thesetting of the next pulse duty of the PWM pulse signal. In this case, incase that a motor rotation quickens suddenly due to the slip of a wheelor the like, the frequency of a motor current waveform increases inaccordance therewith, and thus the motor current can be acquired by ADconversion. However, since the frequency of the motor current waveformis higher than the carrier period, it is not possible to sample asufficient number of times of the motor current value with respect tothe waveform of its sinusoidal wave, and not to follow a PWM waveform ina direction in which the high rotation of the motor in response to thesudden fluctuation of the load is suppressed. In short, as illustratedin FIG. 4, the motor drive current is easily represented by a sinusoidalwave through a PWM pulse in the motor current having a low frequency incase that the motor rotation is slow, but the motor drive current is noteasily represented by a sinusoidal wave through the PWM pulse in themotor current having a high frequency due to a fast motor rotation. Theinfluence of one-time switching of a pulse waveform generation switch onwhich a switching operation is performed increases in accordance withthe comparison result. In order to reduce the influence, the number ofswitching may be increased by increasing the number of times ofsampling. However, in case that the motor rotation becomes too fast withrespect to the carrier period in which the PWM operation is specified,the earliest motor current is not able to be acquired in a sinusoidalshape even in a case where the sampling interval of the motor current isshortened.

Consequently, since the PWM pulse in which the acquired current value isreflected is dependent on the carrier period, a plurality of motorcurrent values or the like acquired as feedback information during thecarrier period have to be arithmetically calculated collectively byfiltering or averaging, to thereby reflect the resultant in a duty ofthe PWM pulse. The arithmetic portions 41 d and 41 q perform thearithmetic operation.

FIG. 5 conceptually illustrates a process in case that the samplingperiod in which the motor current values iv and iw and the electricalangle θ are acquired is made shorter than the carrier period, as such aprocessing method. In the PWM operation, the motor current values iv andiw and the electrical angle θ are sampled multiple times for eachcarrier period to perform the coordinate conversion arithmetic operation(vector arithmetic operation) on the resultants, and the coordinateconversion arithmetic results idm and iqm are aggregated in a comparisontarget for one period of the carrier period by performing apredetermined arithmetic operation such as averaging in the arithmeticportions 41 d and 41 q. The aggregated arithmetic results are reflectedin the setting of the next pulse duty of the PWM pulse signal. Thereby,even in case that the motor rotation quickens suddenly due to the slipof a wheel and thus the frequency of the motor current waveformincreases, a sufficient number of times of the motor current value issampled with respect to the waveform of its sinusoidal wave, and thus itis possible to follow a PWM waveform in a direction in which the highrotation of the motor is suppressed.

Hereinafter, a description will be given of a specific control mode forfollowing a PWM pulse in a direction in which the high rotation of thealternating-current motor due to a drastic load fluctuation issuppressed.

<<First PWM Pulse Follow-up Control Mode for Load Fluctuation>>

A first PWM pulse follow-up control mode will be described. In FIG. 2,functional blocks of the subtracters 30 d and 30 q, the PI arithmeticunits 32 d and 32 q, the coordinate conversion portion 34 and the likeexcept for the accelerator 26 and arithmetic sequence control usingthese blocks are assumed to be realized by the CPU 20 and its operatingprogram. The accelerator 26 is realized by hardware different from theCPU 20.

In FIG. 2, the acquisition period (that is, startup period of an ADconversion operation for the motor currents Iv and Iw) of the motorcurrent values iv and iw in the AD converter 24 is synchronized with thecarrier period of the PWM circuit 23 by the control of the CPU 20.Similarly to this, the acquisition period of the electrical angle θ inthe counter 25 becomes also the same as the startup period of the ADconversion operation. Hereinafter, such a period is simply denoted bythe sampling period of feedback information (motor current values iv andiw and electrical angle θ) in the accelerator 26.

The sampling period of the feedback information is synchronized with thecarrier period of the PWM circuit 23, and the synchronous controlthereof includes synchronous control of the sampling period in the CPUand independent synchronous control of the sampling period in theaccelerator 26, in the present embodiment.

The synchronous control of the sampling period in the CPU 20 is controlconforming the sampling period to the carrier period, that is, controlcapable of once sampling the feedback information (motor current valuesiv and iw) for each carrier period. For example, the startup timing of aconversion operation of the AD conversion circuit 24 is set for eachcarrier period, and the electrical angle θ is output from the counter 25in a period based thereon. Here, the carrier period of the PWM circuit23 is set, in principle, in accordance with a torque command which iscapable of being grasped from a current command value by the CPU 20. Forexample, a loss of PWM pulse drive is reduced even in case that theburden of control increases by decreasing the carrier period at the timeof requiring a large torque, and preferentially, the burden ofcontrolling the PWM pulse drive is not caused to increase by increasingthe carrier period in case that a small torque may be satisfactory.

The independent synchronous control of the sampling period in theaccelerator 26 is control for determining whether the accelerator 26generates a predetermined load fluctuation in the alternating-currentmotor 2, shortening the sampling period of the feedback information(motor current values iv and iw and electrical angle θ) initialized bythe CPU 20 until the high rotation of the alternating-current motor 2subsides (until the PWM waveform is followed up in a direction in whichthe high rotation of the motor is suppressed) in case that the loadfluctuation is determined to be generated, and returning the samplingperiod of the feedback information to a reference value which is aninitialized value in case that the motor control follows the loadfluctuation.

FIG. 6 illustrates a configuration of the accelerator 26 for performingthe synchronous control of the sampling period. The accelerator 26includes a follow-up control portion 42, a load fluctuationdetermination portion 43, correction portions 44 and 45, and registersRG1θ to RG12 t, in addition to the coordinate conversion portion 40 andthe aggregate arithmetic portions 41 d and 41 q. The coordinateconversion portion 40 and the aggregate arithmetic portions 41 d and 41q are an example of an arithmetic circuit 47 that performs an arithmeticoperation for aggregating the feedback information. The follow-upcontrol portion 42 and the load fluctuation determination portion 43 arean example of a control circuit 46 that controls the sampling period ofthe feedback information so as to be variable in case that apredetermined load fluctuation is generated in the alternating-currentmotor 2.

The register RG1θ is supplied with the electrical angle θ which isacquired in the counter 25, and the register RG2 iviw is supplied withthe motor currents iv and iw which are acquired in the AD converter 24.An offset value is set in the registers RG3 ofs and RG4 ofs by a CPU120. The correction portion 44 corrects the motor currents iv and iw,supplied to the register RG2 iviw, to the offset value which is set inthe register RG3 ofs. For example, in case that the AD conversion rangeof the AD converter is set to 0 to 5 V, a process of correcting an ADconversion value obtained thereby to a conversion value centering on 2.5V is performed. The correction portion 45 corrects the electrical angleθ, supplied to the register RG1θ, to the offset value which is set inthe register RG2 ofs. For example, correction for offsettingmisalignment due to a mechanical error such as the rotor position of theresolver 5 is performed. The motor currents iv and iw and the electricalangle θ which are corrected by the correction portions 44 and 45 areconverted into the d-axis current value idm and the q-axis current valueiqm by the coordinate conversion portion 40. The electrical angle θ issupplied to the register RG58, and the electrical angle θ which issupplied to the register RG58 is referenced in synchronization with arequired coordinate conversion timing by the CPU 20 constituting thecoordinate conversion portion 34.

The setting of a startup trigger of an AD conversion operation by the ADconverter 24 is performed on the register REG7 adt by the CPU 20, or isperformed on the register REG7 adt by the follow-up control portion 42.The setting of the register REG7 adt is performed by only the CPU 20 inthe synchronous control of the sampling period in the CPU 20. On theother hand, in the independent synchronous control of the samplingperiod in the accelerator 26, the register REG7 adt which is initializedby the CPU 20 is reset by the follow-up control portion 42, and thus anAD conversion operation period in the AD converter 24 is controlled soas to be variable.

The coordinate conversion portion 40 sequentially performs coordinateconversion in synchronization with the sampling period of the motorcurrent in the AD converter 24, and the d-axis current value idm and theq-axis current value iqm on which the coordinate conversion is performedare subject to a filter arithmetic operation or an averaging arithmeticoperation in the carrier period alone, respectively, in the aggregatearithmetic portions 41 d and 41 q. The averaging arithmetic operationis, for example, a process of performing an arithmetic average or aweighted average on the d-axis current value idm and the q-axis currentvalue iqm in the carrier period alone. The filter arithmetic operationis, for example, a process of setting the d-axis current value idm andthe q-axis current value iqm passing through a bandpass such as abandpass filter, or the average value thereof, to the d-axis currentvalue id and the q-axis current value iq. Gains which are set in theregisters RG8 g and RG9 g are designated in arithmetic processing in thearithmetic portions 41 d and 41 q. For example, a weighted value for theaverage value on which the arithmetic operation is performed isdetermined to be a gain in a case of an arithmetic averaging process,and a weighted value for each of the d-axis current value idm and theq-axis current value iqm is determined to be a gain in a case of aweighted averaging process. In addition, in the filter arithmeticprocessing, a bandpass value or a cutoff value is determined to be again in accordance with the magnitudes of the d-axis current value idand the q-axis current value iq which are immediately preceding filterarithmetic results.

The setting of a corresponding gain is performed on the registers RG8 gand RG9 g by the CPU 20, or is performed on the registers RG8 g and RG9g by the follow-up control portion 42. In the synchronous control of thesampling period in the CPU, the setting of the registers RG8 g and RG9 gis performed by only the CPU 20. On the other hand, in the independentsynchronous control of the sampling period in the accelerator 26, RG8 gand RG9 g which are initialized by the CPU 20 are reset by the follow-upcontrol portion 42. By this resetting, it is possible to cope with adifference in a weight included in one piece of sample data in responseto a change (change in the sampling period of the motor current) in theAD conversion operation period by the AD converter 24, or a differencein an influence which is given to one pulse of the PWM pulse by onepiece of sampling data.

The d-axis current value id and the q-axis current value iq on which thearithmetic operation is performed by the arithmetic portions 41 d and 41q are set in the registers RG10 pid and RG11 kiq, the d-axis currentvalue id and the q-axis current value iq which are set are referenced bythe CPU 20, and the process of the subtracters 30 d and 30 q isperformed.

Although not particularly limited, the load fluctuation determinationportion 43 detects the fluctuation of a motor load on the basis of theq-axis current value iqm which is a component corresponding to a torqueof the motor load. For example, the fluctuation of the motor load isdetected on the basis of the change rate of the q-axis current valueiqm. The detection result thereof is given to the follow-up controlportion 42. In addition, the load fluctuation can also be detected bythe CPU 20 acquiring a detection signal of the sensor (SNSR) 7 of FIG. 1which is disposed outside the microcomputer 1 from the network 6. Forexample, the sensor 7 receives a reflected signal from a vehicletraveling road, and the CPU 20 gives the change of the reflected signalas a road surface state signal RDSI to the follow-up control portion 42.The follow-up control portion 42 predicts a drastic load drop of thealternating-current motor on the assumption of sudden entrance into afreezing road surface or a rainwater road surface on the basis of theroad surface state signal RDST.

In case that a drastic drop of the motor load, that is, a drastic torquedrop is detected on the basis of the detection output of the loadfluctuation determination portion 43 or the road surface state signalRDST, the follow-up control portion 42 starts the autonomous synchronouscontrol of the sampling period in the accelerator 26. Control datarequired for this control is set in the registers RG11 t and RG12 t, forexample, by the CPU 20. For example, the control data is data indicatingthe carrier period of PWM, and data indicating the shortening degree ofthe sampling period of the autonomous synchronous control, the changedegree of the gain, and the like. The follow-up control portion 42refers to such control data from the registers RG11 t and RG12 t, andthus performs the setting of a startup trigger in the register RG7 adt,the setting of gains in the registers RG8 g and RG9 g, and theautonomous synchronous control of the sampling period by controlling theconversion period of the coordinate conversion portion 40.

FIG. 7 illustrates a processing procedure of the autonomous synchronouscontrol of the sampling period together with a synchronous controlprocedure of the sampling period in the CPU. The sampling period of thefeedback information and the gain control of the arithmetic portions 41d and 41 q are aggregated in, for example, steps S1 to S5 of FIG. 7.Step S1 is a process of the CPU. The CPU 20 determines the carrierperiod according to a necessary torque, sets the control data in theregisters RG11 t and RG12 t, initializes the startup trigger of ADconversion, that is, the sampling period in the register REG7 adt inaccordance with the carrier period, and sets the gains in the registersRG8 g and RG9 g. Thereby, the CPU 20 drives and controls thealternating-current motor 2 in accordance with the current commandvalues id and iq while feeding back the motor current.

In case that the alternating-current motor 2 is rotated by the controlof the CPU 20, the load fluctuation determination portion 43 determineswhether a great fluctuation of the motor load is generated from theq-axis current value iqm which is acquired in the coordinate conversionportion 40 (S2). For example, the determination portion determines adrastic drop of the load caused by the high rotation of the motor 2 dueto the slip of a wheel, that is, whether the q-axis current value iqmbecomes equal to or less than a threshold. In case that the loadfluctuation is determined to be great, the load fluctuationdetermination circuit portion 43 sets a load fluctuation flag (notshown). The load fluctuation flag can also be referenced by the CPU 20.In a state where the fluctuation of the motor load is not great, theprocess of step S1 is performed in accordance with the load in thatcase.

In case that the fluctuation of the motor load is great, the follow-upcontrol portion 42 takes charge of the PWM control of thealternating-current motor, and it is determined whether the motorcontrol follows the fluctuation of the load (S3). This determination isperformed, for example, by the load fluctuation determination circuitdetermining whether the q-axis current value iqm becomes larger than thethreshold as described above. In case that the control of the motorcurrent does not follow the fluctuation of the load by restoring thehigh rotation of the motor due to the drastic fluctuation of the load,the drive current of the motor 2 is not formed in a sinusoidal shape,and thus the motor rotation becomes unstable.

In case that the control of the motor current does not follow thefluctuation of the load, the follow-up control portion 42 shortens thesampling period in the carrier period in that case in accordance withthe control data of the register RG12 t, and thus the setting of thegains of the arithmetic portions 41 d and 41 q is changed (S4). Thereby,since the sampling number of the motor current in the carrier periodtends to increase, the drive current based on the PWM pulse can bebrought close to a sinusoidal shape. Thereby, whether the rotation ofthe motor is restored, that is, the control of the motor current followsthe fluctuation of the load is determined successively in step S3. Incase that the following is not yet performed for each determination, thesetting change may be performed so that follow-up responsiveness israised gradually by further shortening the sampling period in step S4.In case that the following is performed, the follow-up control portion42 returns the sampling period and the gain to a state before theoperation in step S4, clears the load fluctuation flag, and entrusts thesynchronous control of the sampling period to the control of the CPU 20.

In the synchronous control of the sampling period in the CPU 20, asillustrated in FIG. 8, the number of times of sampling of the feedbackinformation can also be controlled to multiple times such as four timesin one period of the carrier period. The number of times of sampling maybe determined in accordance with the magnitude of the carrier period,depending on an operating program of the CPU 20.

Further, in the autonomous synchronous control of the sampling period,as illustrated in FIG. 8, in case that a great load fluctuation isdetected in the middle of the carrier period, the sampling period may beshorten halfway.

FIG. 9 illustrates a control mode in the skidding of a wheel and thereturn thereof to a normal rotation. At the time of normal traveling inwhich the skidding is not generated, a torque corresponds to therotational speed of the motor. On the other hand, in case that a torqueis reduced at the time of the skidding of a wheel due to road surfacefreezing, the sudden stepping of an accelerator, or the like, therotational speed of the motor becomes faster. In case that a torqueincreases at the time of the settlement of the skidding, the rotationalspeed of the motor becomes lower. Basic control in the CPU 20 at thetime of the skidding and the settlement of the skidding is as follows.In case that a wheel skids due to a slip or the like, the rotation ofthe motor 20 proceeds, and the load of the motor 20 is reduced. In thiscase, the CPU 20 delays a rise in PWM pulse, adjusts a torque of themotor 20 by performing a process of reducing a duty ratio of the PWMpulse signal, and attempts to restore the rotation speed of the motor20. In that case, the follow-up control portion 42 performs control forgenerating motor current values id and iq based on feedback so as toimprove follow-up responsiveness of the motor control with respect tothe fluctuation of the load by shortening the sampling period inresponse to the sudden fluctuation of the load such as a reduction inthe motor load. Thereafter, in case that the slip is stopped and theskidding of a wheel is settled, the rotation of the motor 20 becomesslower, and the load of the motor 20 increases. Then, the CPU 20quickens a rise timing of the PWM pulse, adjusts a torque of the motor20 by performing a process of increasing the duty ratio of the PWM pulsesignal, and attempts to restore the rotation speed of the motor 20. Inthat case, the follow-up control portion 42 does not respond to a suddenfluctuation of the load such as an increase in the motor load, andentrusts control to the CPU 20.

According to the autonomous synchronous control of the sampling periodin the accelerator 26, the following operational effects are obtained.

(1) The sampling period of the feedback current for a great fluctuationof the motor load is shortened by the accelerator 26 which is separatehardware from the CPU 20, and an arithmetic operation is performed inwhich motor current values obtained thereby are arranged by filtering,averaging or the like, to thereby perform a process of reflecting theresultant in a duty of the PWM pulse. Thereby, even in case that themotor rotation quickens suddenly due to the slip of a wheel and thus thefrequency of the motor current waveform increases, a sufficient numberof times of the motor current value is sampled with respect to thewaveform of its sinusoidal wave, and thus it is possible to follow a PWMwaveform so as to suppress undesired high rotation of the motor. It ispossible to considerably reduce a burden of the CPU 20 in this follow-upcontrol.

(2) Since it is possible to burden the follow-up control portion 42 withcontrol of the acquisition period of the feedback information until thealternating-current motor skids due to a slip or the like and thenrecovers, it is possible to reduce a burden of the CPU 20 in this point.

(3) Since the follow-up control portion 42 senses the predetermined loadfluctuation from the motor current value iqm, it is possible to easilyacquire the fluctuation of the motor load without imposing a burden onthe CPU 20.

(4) In case that the sampling period of the feedback information isshortened, the follow-up control portion 42 changes the gains of thearithmetic portions 41 d and 41 q as necessary, and performs control forrestoring the gains of the arithmetic portions 41 d and 41 q in casethat the sampling period is returned to a reference value. Therefore, itis possible to decrease the gains in accordance with an increase in thenumber of acquisitions of the feedback information so that a responsedoes not become sensitive without imposing a burden on the CPU 20, or tokeep the gains unchanged due to a fast response in case that the numberof acquisitions of the feedback information increases.

(5) Since the accelerator 26 is dedicated hardware which is separatehardware from the CPU 20, the accelerator has a tendency to optimize thenumber of arithmetic bits, the arrangement of registers with respect tothe arithmetic circuit, or the like, and thus is suitable for thespeed-up of data processing. The CPU 20 can also perform higher-speedprocessing at a lower operating frequency and with a small circuitscale, lower power consumption can be achieved than in a case where theCPU is entirely burdened, and it is also contribute to an improvement inthe exothermic characteristics of a product.

(6) Since the feedback information which is fed back to the acceleratoris the motor current values iv and iw which are obtained by performingAD conversion on a current which is fed back from thealternating-current motor 2 and an electrical angle which is obtainedfrom the rotor position of the alternating-current motor 2, the feedbackinformation is suitable for vector control of the alternating-currentmotor 2.

(7) Separately from the follow-up control of the follow-up controlportion 42, the CPU 20 requires setting control of the carrier period ofthe PWM circuit 23 in accordance with a relationship with a rotationtorque required for the feedback control, and thus it is economical, inview of a system, for the CPU 20 to initialize a period in which thefeedback information is acquired in the relationship with the rotationtorque.

(8) Separately from the follow-up control of the follow-up controlportion 42, the CPU 20 also requires gain setting in response to thesetting of the carrier period of the PWM circuit 23 in accordance withthe relationship with the rotation torque required for the feedbackcontrol, and thus it is economical, in view of a system, for the CPU 20to initialize the gains of the arithmetic portions 41 d and 41 q in therelationship with the rotation torque.

(9) The follow-up control portion 42 predicts the predetermined loadfluctuation from the state detection information RDST of a travelingsurface that receives a rotational force of the alternating-currentmotor, and thus motor rotation control for suppressing a suddenfluctuation of the motor load can be performed by faster reaction.

(10) The follow-up control portion 42 controls an AD conversion startuptrigger interval of AD conversion processing of a current to be fed backand a fetching interval of the rotor rotation angle value to thearithmetic circuit, to thereby determine a period in which the feedbackinformation is acquired, and thus it is possible to easily control thesampling period of the feedback information for obtaining the feedbackinformation without imposing a burden on the CPU 20 in the follow-upcontrol.

<<Second PWM Pulse Follow-up Control Mode for Load Fluctuation>>

In the first PWM pulse follow-up control mode, a description has beengiven on the assumption that the follow-up control portion 42 does notperform a change in the carrier period determined by the CPU 20. In asecond PWM pulse follow-up control mode, the carrier period as well asthe sampling period can be changed with respect to a sudden fluctuationof the load.

FIG. 10 illustrates an operation example in case that the carrier periodis changed together with the sampling period with respect to a suddenfluctuation of the load. In case that there is a sudden fluctuation ofthe load, only the number of times of sampling of the feedbackinformation is increased first in the process of step S4 of FIG. 7,without changing the carrier period. Thereby, in case that it isdetermined that the motor control does not follow the load fluctuation(S3), follow-up responsiveness may have a tendency to be improved bylengthening the carrier period and increasing the number of times ofsampling in the next step S4.

<<Third PWM Pulse Follow-up Control Mode for Load Fluctuation>>

In the first PWM pulse follow-up control mode, a description has beengiven on the assumption that the sampling period of the feedbackinformation is shortened only in case that there is a sudden fluctuationof the load. In a third PWM pulse follow-up control mode, the number oftimes of sampling within the carrier period is made variable inaccordance with the motor load (motor rotation speed) in the synchronouscontrol of the sampling period in the CPU 20.

In the synchronous control of the sampling period in the CPU 20, asillustrated in FIG. 11, the feedback information is sampled at the rateof one time per period of the carrier period from the low speed of themotor rotation to the medium speed thereof, and the feedback informationis sampled at the rate of four times per period of the carrier period atthe high speed of the motor rotation. The number of times of samplingmay be determined in accordance with the motor rotation, depending onthe operating program of the CPU 20. In case that there is a drasticload fluctuation in a state of the high rotation, the responsiveness ofthe PWM control for restoring the motor rotation by further shorteningthe sampling period is improved by the synchronous control of thesampling period in the accelerator 26.

<<Fourth PWM Pulse Follow-up Control Mode for Load Fluctuation>>

In the first PWM pulse follow-up control mode, the follow-up controlportion 42 is adopted giving top priority to a reduction in the controlburden of the CPU 20, and the operations of the coordinate conversionportion 40 and the arithmetic portions 41 d and 41 q which are dedicatedarithmetic circuits are controlled. In a fourth PWM pulse follow-upcontrol mode, on the assumption that there is a margin capable ofburdening the CPU 20A with only the control thereof, the CPU 20A iscaused to execute the control.

In this case, as illustrated in FIG. 12, in an arithmetic circuit 26A,the CPU 20A is burdened with a control function of the follow-up controlportion 42 and a determination function of the load fluctuationdetermination portion 43. The CPU 20A is configured to be capable ofreferring to the motor current value iqm through the register RG13 iqm.The coordinate conversion portion 40 performs coordinate conversion at anecessary timing by the carrier period and the sampling period in thatcase being transferred by control data which is set in the register RG14sync, from the CPU 20A. Naturally, the CPU 20A performs a settingoperation of a startup trigger for the register RG7 adt for shorteningthe sampling period at time of the load fluctuation and a settingoperation of gains for the registers RG8 g and RG9 g correspondingthereto.

Meanwhile, other configurations in the fourth PWM pulse follow-upcontrol mode are the same as those of the first PWM pulse follow-upcontrol mode, and thus the detailed description thereof will not begiven. The second and third PWM pulse follow-up control modes can alsobe applied to the fourth PWM pulse follow-up control mode.

According to the fourth PWM pulse follow-up control mode, as representedby FIG. 6, a burden of the CPU 20A increases in the control of theacquisition period of the feedback information as compared to a casewhere the follow-up control portion 42 is adopted, but it is possible tocope with the burden flexibly through software of the CPU 20A.

As described above, while the invention devised by the inventor has beendescribed specifically based on the embodiments thereof, the inventionis not limited to the embodiments, and it goes without saying thatvarious changes and modifications may be made without departing from thescope of the invention.

For example, the arithmetic unit in which the accelerator has beendescribed as an example can also be configured to use all or some ofarithmetic functions of a general-purpose DSP or the like. An aggregatearithmetic processing function in the arithmetic unit is not limited tofiltering or averaging, and can be appropriately changed. The statedetection information of the traveling surface is not limited to achange in the reflectance of a road surface, and a shake or the likeresponding to the irregularities of a road surface may be detected. Themotor control device is not limited to a one-chip microcomputer, and maybe a mulita-chip semiconductor module or the like. The rotation angledetection of the motor shaft is not limited to use of the resolver.

INDUSTRIAL APPLICABILITY

The invention can be widely applied to not only an automobile such as anEV or an HV, but also a motor-driven train and other machinery andappliances using a motor as a drive source.

EXPLANATION OF REFERENCE NUMERALS

-   -   1: motor drive device    -   2: alternating-current motor (MT)    -   3: transmission    -   4: wheel    -   5: resolver    -   6: in-vehicle network    -   7: sensor (SNSR)    -   10: inverter    -   11: pre-driver    -   12: resolver digital converter    -   13: microcomputer (MCU)    -   14: current sensor    -   Iv, Iw: motor current    -   Smg: excitation signal    -   Srs: resolver signal    -   Rp: motor rotation phase signal of layer U, V, and W    -   20, 20A: CPU    -   21: internal memory (MRY)    -   22: network controller (COM)    -   23: PWM circuit (PWM)    -   24: AD converter (ADC)    -   25: counter (COUNT)    -   26, 26A: accelerator (ACCL)    -   27: internal bus    -   iv, iw: motor current value    -   θ: electrical angle (rotor rotation angle value indicating rotor        position of motor)    -   id: d-axis current command value    -   iq: q-axis current command value    -   30 d, 30 q: subtracter    -   idc: present d-axis current value    -   iqc: present q-axis current value    -   Δid, Δiq: deviation    -   32 d, 32 q: PI arithmetic unit    -   Vd: d-axis voltage command    -   Vq: q-axis voltage command    -   34: coordinate conversion portion    -   Vu, Vv, Vw: 3-phase motor drive voltage command    -   Pu, Pv, Pw: PWM pulse signal    -   40: coordinate conversion portion    -   idm: d-axis current value    -   iqm: q-axis current value    -   41 d, 41 q: aggregate arithmetic portion    -   46: control circuit    -   47: arithmetic circuit

What is claimed is:
 1. A motor control device comprising: a PWM circuitfor performing switch control on an inverter that outputs a drivecurrent to an alternating-current motor through a PWM pulse signal; aCPU that performs feedback control on a duty of the PWM pulse signal;and an arithmetic unit, in which a sampling period of feedbackinformation is made variable, and which performs predeterminedarithmetic processing for aggregating the feedback information acquiredin the sampling period shorter than a carrier period of the PWM circuitin a comparison target for one period of the carrier period in case thata predetermined load fluctuation is generated in the alternating-currentmotor, wherein the CPU controls the duty of the PWM pulse signal afterthe predetermined load fluctuation is generated, on the basis of anarithmetic result in the arithmetic unit and a drive command value. 2.The motor control device according to claim 1, wherein the feedbackinformation is a motor current value which is obtained by performing ADconversion on a current which is fed back from an alternating-currentmotor and a rotor rotation angle value which is obtained from a rotorposition of the alternating-current motor.
 3. The motor control deviceaccording to claim 2, wherein in case that a predetermined loadfluctuation is generated in the alternating-current motor, the controlunit includes a control circuit that controls a sampling period offeedback information so as to be variable, and an arithmetic circuitthat performs the predetermined arithmetic processing, and the controlcircuit determines whether a predetermined load fluctuation is generatedin the alternating-current motor, shortens a period in which thefeedback information is acquired until control of thealternating-current motor follows the load fluctuation in case that theload fluctuation is determined to be generated, and performs control forreturning the period in which the feedback information is acquired to areference value in case that the control of the alternating-currentmotor follows the load fluctuation.
 4. The motor control deviceaccording to claim 3, wherein the CPU initializes the period in whichthe feedback information is acquired, and the control circuit sets theinitialized period to a control target.
 5. The motor control deviceaccording to claim 4, wherein the control circuit senses thepredetermined load fluctuation from the rotor rotation angle value orthe motor current value.
 6. The motor control device according to claim4, wherein the control circuit further predicts the predetermined loadfluctuation from state detection information of a traveling surface thatreceives a rotational force of the alternating-current motor.
 7. Themotor control device according to claim 3, wherein the predeterminedarithmetic processing in the arithmetic circuit includes coordinateconversion processing for converting the motor current value and therotor rotation angle value into a two-phase current value, and filterarithmetic processing or average arithmetic processing for the two-phasecurrent value on which coordinate conversion is performed.
 8. The motorcontrol device according to claim 7, wherein the control circuit furtherchanges a gain of the filter arithmetic processing or the averagearithmetic processing in the arithmetic circuit, as necessary, in casethat the period in which the feedback information is acquired is set tobe short, and performs control for returning the gain of the filterarithmetic processing or the average arithmetic processing to theinitial value in case that the period in which the feedback informationis acquired is returned to the reference value.
 9. The motor controldevice according to claim 8, wherein the CPU initializes the gain of thefilter arithmetic processing or the average arithmetic processing, andthe control circuit sets the initialized gain to a control target. 10.The motor control device according to claim 7, wherein the controlcircuit controls an AD conversion startup trigger interval of ADconversion processing of the fed-back current and a fetching interval ofthe rotor rotation angle value to the arithmetic circuit, to therebydetermine the period in which the feedback information is acquired. 11.The motor control device according to claim 2, wherein the control unitincludes the arithmetic circuit that performs the predeterminedarithmetic processing, and the CPU controls a sampling period offeedback information so as to be variable, determines whether apredetermined load fluctuation is generated in the alternating-currentmotor, shortens a period in which the feedback information is acquireduntil control of the alternating-current motor follows the loadfluctuation in case that the load fluctuation is determined to begenerated, and returns the period in which the feedback information isacquired to a reference value in case that the control of thealternating-current motor follows the load fluctuation.
 12. The motorcontrol device according to claim 11, wherein the CPU senses thepredetermined load fluctuation from the rotor rotation angle value orthe motor current value.
 13. The motor control device according to claim12, wherein the CPU further predicts the predetermined load fluctuationfrom state detection information of a traveling surface that receives arotational force of the alternating-current motor.
 14. The motor controldevice according to claim 11, wherein the predetermined arithmeticprocessing in the arithmetic circuit includes coordinate conversionprocessing for converting the motor current value and the rotor rotationangle value into a two-phase current value, and filter arithmeticprocessing or average arithmetic processing for the two-phase currentvalue on which coordinate conversion is performed.
 15. The motor controldevice according to claim 14, wherein the CPU changes a gain of thefilter arithmetic processing or the average arithmetic processing in thearithmetic circuit, as necessary, in case that the period in which thefeedback information is acquired is set to be short, and performscontrol for returning the gain of the filter arithmetic processing orthe average arithmetic processing to the initial value in case that theperiod in which the feedback information is acquired is returned to thereference value.
 16. The motor control device according to claim 14,wherein the CPU controls an AD conversion startup trigger interval of ADconversion processing of the fed-back current and a fetching interval ofthe rotor rotation angle value to the arithmetic circuit, to therebydetermine the acquisition period of the feedback information.
 17. Themotor control device according to claim 1, wherein the motor controldevice is constituted by a microcomputer which is formed as asemiconductor integrated circuit in a silicon substrate.
 18. A motordrive device that drives an alternating-current motor for vehicletraveling, comprising: an inverter that supplies a motor current to thealternating-current motor; and a motor control device that performsfeedback control on a motor current which is output by the inverter onthe basis of a drive command value, wherein the motor control deviceincludes a PWM circuit that performs switch control on the inverterthrough a PWM pulse signal, a CPU that performs feedback control on aduty of the PWM pulse signal, and an arithmetic unit, in which asampling period of feedback information is made variable, and whichperforms predetermined arithmetic processing for aggregating a pluralityof pieces of the feedback information acquired in the sampling periodshorter than a carrier period of the PWM circuit in a comparison targetfor one period of the carrier period in case that a predetermined loadfluctuation is generated in the alternating-current motor, and the CPUcontrols the duty of the PWM pulse signal after the predetermined loadfluctuation is generated, on the basis of an arithmetic result in thearithmetic unit and the drive command value.
 19. The motor drive deviceaccording to claim 18, wherein the feedback information is a motorcurrent value which is obtained by performing AD conversion on a currentwhich is fed back from the alternating-current motor and a rotorrotation angle value which is obtained from a rotor position of thealternating-current motor.
 20. The motor drive device according to claim19, wherein the control unit includes a control circuit that controls asampling period of feedback information so as to be variable in casethat a predetermined load fluctuation is generated in thealternating-current motor, and an arithmetic circuit that performs thepredetermined arithmetic processing, and the control circuit determineswhether a predetermined load fluctuation is generated in thealternating-current motor, shortens a period in which the feedbackinformation is acquired until control of the alternating-current motorfollows the load fluctuation in case that the load fluctuation isdetermined to be generated, and performs control for returning theperiod in which the feedback information is acquired to a referencevalue in case that the control of the alternating-current motor followsthe load fluctuation.